A Novel Semi-airborne EM System for Mineral Exploration - First Results from Combined Fluxgate and Induction Coil Data

A novel semi-airborne frequency domain system is developed within the DESMEX project. The system is designed to achieve a penetration depth of about 1km with an areal coverage of about 6×6km² per source installation on the ground. Here, we report on first results achieved with the new system. Horizontal electric dipole transmitters were used to inject time-varying electrical currents into the ground, and both a three-axis induction coil set up (Metronix MFS-11e) and a fluxgate (Bartington MAG-03) were installed on a helicopter-towed platform. We measure the induced magnetic field in the air in a frequency range from 1Hz to 10kHz. Additionally recorded attitude data can be used for correction of motion noise and for in-flight calibration to determine orthogonality and scaling errors in the fluxgate data as well as orientation errors of all sensors within the bird. In a first flight test the corrected fluxgate data shows a good signal-to-noise-ratio in the range 10-400Hz with a noise level generally below 50pT/√Hz. The coils yield superior noise levels of less than 1pT/√Hz at frequencies higher than 400Hz. Frequency-domain response functions between the magnetic field and the source current are found to be consistent with subsurface conductivity structures.